1. Field of the Invention
The present invention relates to a device for measuring a stiffness of a golf-club shaft and, more particularly, to a device for directly measuring a stiffness of the club shaft, which is a combination of flexure strength and torsion strength.
2. Description of the Related Art
Generally, a golf-club shaft is subjected to flexure and torsion when swung during play or practice. A golf player feels the degree of flexure and torsion as a shaft stiffness. A club shaft having small flexure and torsion has a stiff feel, and a club shaft having large flexure and torsion has a soft feel. Generally, a player having a strong swing can move a club shaft at a high head speed, and thus a stiffer club shaft, i.e., a shaft having small flexure and torsion, is more suitable for such a player. A player with a weak swing, however, moves a club shaft at a low head speed, and thus a softer shaft, i.e., a shaft having large flexure and torsion is more suitable for such a player.
Conventionally, a device for measuring only a flexure strength of a golf-club shaft has been proposed and used, and a device for measuring only a torsion strength of a golf-club shaft also has been proposed and used. Accordingly, to inspect a stiffness of a golf-club shaft, it has been necessary to separately measure the flexure strength and torsion strength of a club shaft by using two different devices and to estimate a stiffness of the shaft based on the measurement values. Consequently, there is a demand for a method of directly measuring a stiffness of a golf-club shaft.